The　present　work　attempts　to　investigate　the　sintering　characteristics,　grain　boundary　morphology　and　electric　conductivity　of　Nb2O5　doped　TiO2　semiconductor　ceramics.　X-ray　diffraction　results　showed　evidence　of　a　second　phase　beside　the　rutile　TiO2　when　Nb2O5　exceeds　0.7　mol%.　SEM　images　showed　that　Nb2O5　doping　can　lowers　the　sintering　temperature　of　TiO2,　although　not　significantly.　Lattice　images　of　the　grain　boundary　morphology　obtained　by　high　resolution　transmission　electron　microscopy　revealed　defects　introduced　from　the　doping.　Grain　boundaries　vary　from　amorphous　to　a　faceted　structure.　Finally,　electrical　conductivity　measurements　showed　that　the　grain　boundary　resistance　is　greatly　reduced　at　high　temperature.　(c)　2006　Elsevier　B.V.　All　rights　reserved.